Difference between oracle DATE and TIMESTAMP
DATE and TIMESTAMP have the same size (7 bytes). Those bytes are used to store century, decade, year, month, day, hour, minute and seconds. But TIMESTAMP allows to store additional info such as fractional seconds (11 bytes) and fractional seconds with timezone (13 bytes).
TIMESTAMP was added as an ANSI compliant to Oracle. Before that, it had DATE only.
In general cases you should use DATE. But if precision in time is a requirement, use TIMESTAMP.
And about Java, the oracle.sql.DATE class from Oracle JDBC driver, provides conversions between the Oracle Date/Timestamp data type and Java classes java.sql.Date, java.sql.Time and java.sql.Timestamp.